Conformable insulation

ABSTRACT

This disclosure relates to a unitary insulating member comprised of a plurality of strips of creped kraft paper intermittently fastened together by a thermosettable resin adhesive and compressed to a density higher than that of any single creped strip. The bonded unitary member has a high dielectric strength and a large degree of the resilient and conformable properties of its constituent crepe paper strips.

United States Patent Heinrichs, Jr. et al.

[54] CONFORMABLE INSULATION [72] Inventors: Frank W. l-leinrichs, Jr., McMurray; Alex F. Polasky, Canonsburg; Charles C. Honey; Lawrence R. Toothman, both of Pittsburgh, all of Pa.

[73] Assignee: McGraw-Edison Company, Elgin,

[22] Filed: March 12, 1969 [21] Appl. No.: 806,517

[52] U.S. Cl. ..l74/l38 E, 156/291, 161/99, 161/129,161/148, 310/215, 336/209 [51] Int. Cl ..H0lf 27/36 [58] Field of Search ..-161/129, 146,148, 99; 174/1383, 138 E; 310/215; 336/209 [56] References Cited UNITED STATES PATENTS 1,992,215 2/1935 Kellet ..161/l29 X 15 3,681,516 51 Aug. 1, 1972 2,143,911 l/l939 Fourness ..l61/l29 X 2,315,818 4/1943 Sackner ..l6l/l29 X 3,189,681 6/1965 Feather ..310/2l5 X 3,483,071 12/1969 Frick et al ..'..l6l/l29 2,119,482 5/1938 Huffer ..l6l/l29 X Primary Examiner-Roger F Burnett Assistant Examiner-Raymond O. Linker, Jr. Attorney-Charles F. Lind 57 ABSTRACT This disclosure relates to a unitary insulating member comprised of a plurality of strips of creped kraft paper intermittently fastened together by a thermosettable resin adhesive and compressed to a density higher than that of any single creped strip. The bonded unitary member has a high dielectric strength and a large degree of the resilient and conformable properties of its constituent crepe paper strips.

" 6 Claims, 6 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to insulation for electrical apparatus and in particular to a conformable insulation for use in insulating transformer coils.

In electrical apparatus, such as transformers, a large quantity of built-up pressboard spacing and insulating structures of a great variety of dimensions and shapes is required. Such built-up structures are particularly useful for insulating the live portions of transformers from the casing and for separating the electrical elements from one another. One type of insulating member for transformers and like electrical apparatus are angled channel members utilized to insulate the inside and outside corners of transformer coils. Such insulating members are particularly useful in insulating the flat, substantially rectangular coils of the pancake type.

In the past, such insulating structures have comprised a special grade of pressboard or fuller board which has been soaked in water and worked by hand into a condition such that a cold-pressed preform can be prepared therefrom. After drying of the preform, the desired final structure was obtained by moistening the preform and hot pressing it in a suitably formed mold. As may be readily understood, such an insulating member required a number of steps in its manufacture and a great amount of accuracy in making the structure since it could not be formed to the transformer coil once the molding was finished. Another type of known insulating member is fonned from a plurality of stacked strips of crepe paper each coated with a layer of thermoplastic resin adhesive and bonded into a unitary insulating member at a high pressure and temperature. This type of insulating member is molded to the final shape desiredat the same time that it is bonded and, although it has some small amount of flexibility after molding, it is not resilient or conformable to the transformer coils subsequent to its molding.

It is an object of this invention to provide an insulating member which may be economically manufactured and which is resilient and conformable subsequent to forming to the electrical element which it insulates.

Another object of the invention is to provide a unitary insulating member formed from layers of crepe paper which is resilient and conformable subsequent to its forming and which has a density greater than that of any one of its crepe paper layers.

Another object of the invention is to provide a unitary insulating member which may be formed by hand to the electrical element it is to insulate subsequent to its forming.

A further object of the invention is to provide a unitary insulating member of intermittently bonded strips of crepe paper having a higher density than that of any of its constituent strips of crepe paper and retaining its mechanical properties throughout a temperature range from room temperature to the operating temperature of a transformer.

A further object of the invention is to provide a uni tary insulating member of bonded crepe paper for simultaneously insulating the corners of an electrical coil and spacing the electrical coil from adjacent coils.

2 SUMMARY OF THE INVENTION The objects of this invention are accomplished by providing a plurality of strips of a creped kraft paper intermittently fastened together by a thermosettable resin adhesive and compressed to a density higher than that of any single creped strip. The resulting unitary insulating member has a high dielectric strength while at the same time retaining a large degree of the resilient and conformable properties of its constituent crepe paper strips.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an insulator member having an L-shaped cross-section and being bent toward the inside of the L-shaped cross-section;

FIG. 2 is a perspective view of the insulator member shown in FIG. 1 bent toward the outside of the L- shaped cross-section;

FIG. 3 is across-sectional view taken along line 33 in FIG. 1 showing a portion of the crepe paper layers of the insulator member in an unstretched and uncompressed condition;

FIG. 4 is a cross-sectioned view taken along line 4-4 of FIG. 2 showing a portion of the crepe paper layers of the insulator member in a stretched condition;

FIG. 5 shows another embodiment of the insulator member of the invention; and

FIG. 6 is a plan view of a transformer pancake coil showing insulator members positioned along its inside and outside perimeter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1 of the drawing, a unitary insulator member 2 is shown as comprising a plurality of crepe paper strips bonded together and molded in the cross-sectional form of an L-shape. In this form, the insulator 2 includes the side walls 16 and 18. The crepe paper strips are identified by the number 4 and are best shown in the views of FIGS. 3 and 4. The crepe paper utilized in the insulator member 2 may be of a creped kraft paper having a density of about 0.2 to 0.4 grams per cubic centimeter and approximately 5 mils base thickness. Each of the strips 4 are creped in a direction transverse to the length of the strips and have approximately an percent stretch in the direction of the length of the strips.

A portion of the crepe paper plies or strips 4 of insulator member 2 are shown in FIGS. 3 and 4. The strips 4 are stacked and fastened together and virtually any number of strips 4 may be stacked and fastened or bonded as shown in FIGS. 3 and 4. The strips 4 are held together by an adhesive coating 6 which may be continuously or intermittently applied to at least wide surfaces 8 of each strip 4 so that there is an adhesive coating 6 between each two adjacent strips 4. Although the adhesive coating may be continuous, adjacent strips 4 will adhere or be fastened to each other only at random and intermittent locations 12 along the length of the strips 4. The greatest occurrence of the fastened locations 12 are where projections such as crimp projections 10 in either of two adjacent crepe strips 4 are compressed against the other strips 4 during the form ing of the unitary member 2. Due to only the intermittent adhering of the plies or strips 4 to each other, each of the strips 4 retains a part of their elastic or resilient qualities so that the member 2 will also be resilient and conformable subsequent to its forming. The unitary member 2 is resilient in that it may be formed in various adjacent strips 4. Furthermore, the member 2 may be formed in lateral cross-sections other than the L-shape shown in FIGS. 1 and 2 without affecting the above described resiliency. For example, the unitary member 2 may be deformed transverse to its length toward the inside or outside of its L-shaped cross-section, as respectively shown in FIGS. 1 and 2,. without permane'nt deformation of its longitudinal configuration.

Due to the intermittent adhering of the adjacent crepe strips 4 at the adhered locations 12, the unitary insulator member 2 will have the resilience described above. At the same time, however, there are sufficient adhered locations 12 to hold the stacked strips 4 together and permit their compression and densification into member 2. Densification of the stacked strips 4 occurs where projections of one strip 4 nestle in crimp cavities 14 of an adjacent strip 4. The nestling of projections 10 in cavities 14 occurs between locations 12 where projections 10 have fastened adjacent strips 4 together and many of the nestled projections 10 and cavities 14 will be movable relative to each other so that resilience of the member 2 is not prevented by its densification. The extent of the nestling of projections 10 and cavities 14 determines, in part, the density of the member 2. The density of the member 2 formed under the pressure and temperature described hereinbelow is between 0.7 to 1.0 grams per cubic centimeter as compared to a density of each of strips 4 of about 0.2 to 0.4 grams per cubic centimeter. Thus, the insulator member 2 has a high density and relatively high dielectric strength while at the same time having a resilience subsequent to its forming which permitsit to be conformed to the shape of transformer coils and structures requiring electrical insulation.

The adhesive utilized to maintain the insulator member 2 unitary may be a heat activated, thermosettable resin adhesive such as that known by the commercial designation as Sterling Y-358 or the thermosettable resin adhesive described in copending application Ser. No. 601,292, filed Nov. 21, 1966, and assigned to the assignee of the instant invention. The coating 6 of one of these resin adhesives is applied to each of the paper strips 4 in such a manner that the coating or film thickness of the coating 6 on each strip 4 will be from about 0.8 mils and 2.0 mils after the liquid adhesive has dried and before heating and compressing of the stacked strips to form the unitary member 2. The use of a thermosettable resin in bonding the insulator member 2 together is advantageous since a thermosettable resin remains rigid throughout a temperature range from room temperature through the normal operating temperatures of transformers in which the insulator member 2 may be used. The continued rigidity of the thermosettable resin throughout this temperature range allows the member 2 to be resilient at lower temperatures while still allowing the member 2 to maintain its mechanical strength at higher transformer operating temperatures.

The steps of forming the insulator member 2- include coating each of the crepe paper strips 4 with the thermosettable adhesive coating '6 described above and stacking a plurality of the strips 4. In actual practice, these steps may be accomplished by coating a continuous strip of crepe paper with a heat'activated, thermosettable adhesive, partially curing the adhesive and winding the coated strip onto a number ofindividual rolls (not shown). The rolls-may be then simultaneously unwound with their wide surfaces in a substantially parallel relationship. While in this position, the coated strips are advanced into a mold (not shown) and simultaneously subjected to a pressure of from about 10 to 20 pounds per squareinch and a temperature of from about 128 to 132C. for a period of from about 5 to 8 minutes to produce a unitary insulator member 2 such as shown in FIGS. 1 and 2. The mold (not shown) may have a shapewhich will form the member 2 into a configuration having the L-shape cross section as shown in FIGS. 1 or 2 or any of a variety of other shapes such as a U-shape.

An alternate embodiment of the insulator is the insulator member 20 shown in FIG. 5. The insulator member 20 has substantially the same construction and is formed in the same manner as the insulator member 2, except that subsequent to forming, the fingers 22 on insulator member 20 may be formed by cutting away the excess material around fingers 22. v

Use of the insulator members 2 and 20 with a transformer pancake coil 30 is' shown in 'FIG. 6. An insulator member 2 is shown along theinner periphery of pancake coil 30 so that at the curves of the inner periphery of the coil 30 the insulator member 2 bends in a direction to the outside of its cross-sectional L-shape. An insulator member 20 is shown in engagement with the pancake coil 30 along its outer periphery with the fingers 22 being positioned parallel to the sides of the coil 30. In these positions, the fingers 22 serve to space an adjacent pancake coil (not shown) such as coil 30 when they are stacked together.

While only two specific embodiments of the invention have been shown herein, it will be realized that many modifications thereof are feasible without departing from the spirit and scope of the invention. It is consequently intended in the appended claims to cover all such variations and modifications as fall within the true spirit and scope of the invention.

Iclaim:

l. A unitary insulator member comprising a plurality of stacked and compressed strips of crepe paper each creped in directions transverse to the length of the strip, rigid adhesive between and engaging each adjacent pair of said strips, said adjacent pair of strips being intermittently fastened together along their lengths by said adhesive whereby said member is held unitary, having a predetermined longitudinal configuration and a wall having an L-shaped cross-section transverse to the longitudinal configuration, said member having a resilience in directions perpendicular and parallel to said wall and parallel to the length of the member permitting return of the member to said configuration when the member is deformed from said configuration.

2. The combination according to claim 1 wherein said adhesive is of a thermosettable resin type.

3. A unitary electrical insulator member for an electrical transformer including an electrical coil having a periphery curved along at least a portion thereof, said insulator member comprising a plurality of stacked and compressed strips of crepe paper having creped projections in directions transverse to the length of the strips, said member having a straight longitudinal configuration and including a wall having an angular cross-section in a plain perpendicular to the length of the member, said member being deformable from said straight longitudinal configuration to a right angle longitudinal configuration having the same curvature as the curved portion of the periphery of the transformer coil and being resiliently returnable to said straight longitudinal configuration.

4. The combination according to claim 3 wherein each of said strips of crepe paper have adensity of between 0.2 and 0.4 grams per cubic centimeter and said member has a density of between 0.7 and 1.0 grams per cubic centimeter.

5. A unitary electrical insulator member for an electrical transformer comprising a plurality of stacked and compressed strips of crepe paper having creped projections in directions transverse to the length of the strips, a rigid adhesive between each one of said strips and the strips most adjacent the one strip, said adhesive intermittently rigidly fastening the one strip along its length to said most adjacent strips, each of said strips of said crepe paper having a density of between 0.2 and 0.4 grams per cubic centimeter and said member has a density of between 0.7 and 1.0 grams per cubic centimeter, said member having a predetermined longitudinal configuration and including a wall having an angular crosssection in a plane perpendicular to the length of the member, said member also having a resilience in directions parallel to said cross-section plane permitting return of the member to said longitudinal configuration when the member is deformed from the longitudinal configuration.

6. The combination according to claim 5 wherein said adhesive has a continuous coating thickness on each of said strips sufficient to permit only intermittent fastening together of adjacent strips. 

1. A unitary insulator member comprising a plurality of stacked and compressed strips of crepe paper each creped in directions transverse to the length of the strip, rigid adhesive between and engaging each adjacent pair of said strips, said adjacent pair of strips being intermittently fastened together along their lengths by said adhesive whereby said member is held unitary, having a predetermined longitudinal configuration and a wall having an Lshaped cross-section transverse to the longitudinal configuration, said member having a resilience in directions perpendicular and parallel to said wall and parallel to the length of the member permitting return of the member to said configuration when the member is deformed from said configuration.
 2. The combination according to claim 1 wherein said adhesive is of a thermosettable resin type.
 3. A unitary electrical insulator member for an electrical transformer including an electrical coil having a periphery curved along at least a portion thereof, said insulator member comprising a plurality of stacked and compressed strips of crepe paper having creped projections in directions transverse to the length of the strips, said member having a straight longitudinal configuration and including a wall having an angular cross-section in a plain perpendicular to the length of the member, said member being deformable from said straight longitudinal configuration to a right angle longitudinal configuration having the same curvature as the curved portion of the periphery of the transformer coil and being resiliently returnable to said straight longitudinal configuration.
 4. The combination according to claim 3 wherein each of said strips of crepe paper have a density of between 0.2 and 0.4 grams per cubic centimeter and said member has a density of between 0.7 and 1.0 grams per cubic centimeter.
 5. A unitary electrical insulator member for an electrical transformer comprising a plurality of stacked and compressed strips of crepe paper having creped projections in directions transverse to the length of the strips, a rigid adhesive between each one of said strips and the strips most adjacent the one strip, said adhesive intermittently rigidly fastening the one strip along its length to said most adjacent Strips, each of said strips of said crepe paper having a density of between 0.2 and 0.4 grams per cubic centimeter and said member has a density of between 0.7 and 1.0 grams per cubic centimeter, said member having a predetermined longitudinal configuration and including a wall having an angular cross-section in a plane perpendicular to the length of the member, said member also having a resilience in directions parallel to said cross-section plane permitting return of the member to said longitudinal configuration when the member is deformed from the longitudinal configuration.
 6. The combination according to claim 5 wherein said adhesive has a continuous coating thickness on each of said strips sufficient to permit only intermittent fastening together of adjacent strips. 